How to Build a Dipole Antenna for TVby Thomas Edward
Making a simple half-wave folded dipole TV antenna is an easy construction project. It provides a lot better reception than the simple rabbit ears dipole, but not as good as a high-gain directional antenna. Custom design it for your weakest signal or build several for channels of interest. The antenna is made from "300-ohm twin-lead" which is the brown or black flat lead in wire used for outdoor TV and FM radio antennas.
Cut a piece of flat lead to the desired specific length (which will be 1/2 the wavelength of the TV channel you want to optimize the antenna to receive). The folded dipole is a loop antenna in the shape of a "T". The length of the T's top section is cut to be a half wavelength of the TV station's broadcast frequency in meters (See Reference). For example, the frequency of channel 2 is 57 MHz so the wavelength or the twin lead length is 5 meters. If one folds this in half the top of the "T" will be 2.5 meters long. Simply follow the formula in the reference to determine the desired length for TV station you want your antenna optimized to receive (though the antenna will work for all stations).
Using the example above for channel 2, the twin-lead wire should be cut to 2.5 meters, which is half the wavelength of channel 2's frequency. Strip off about an inch of insulation on both ends and twist them together. Solder these connections.
Find the midpoint of twin-line piece between the two soldered ends. Cut one of the conductors at the midpoint and open up the two wires on each side of the cut, stripping about 1 inch of insulation from each cut end. Take another piece of twin-lead that will be the lead-in wire from the antenna to the TV set, and strip about 1 inch of insulation from the two wires in the twin lead. Wrap one of the wires of the lead-in wire to one of the wires on the T, and wrap the other wire in the twin lead to the other wire on the T. Solder them in place.
Tape all four soldered connections. This will electrically insulate the antenna from other objects.
Antenna should be mounted with the "T" section facing toward TV station. Avoid mounting the antenna near metal and avoid long runs of the lead-in twin-line close to metal. Also avoid coiling the lead-in wire. Attic locations are acceptable or try running it out a window or an outside location. Try moving it about for best performance. If the TV does not have a 300-ohm input (this will be two screw terminals), use a 300-ohm to 75-ohm matching transformer, available at your local electronics store.
- Signal strength and image distortion can be improved using a reflector and possibly a director to your antenna. Use a single piece of uninsulated wire 5 percent longer than the dipole and mount it parallel to and about .2 wavelengths (in air) on the opposite side from the TV station. This is a reflector. A director is a similar piece of wire 5 percent shorter than the dipole and parallel to it on the side toward the station and about 0.15 wavelengths (in air) from the antenna. No electrical connection exists and they are physically independent.
- Take care in operating hot soldering equipment. Avoid dropping molten solder on skin or clothing.
- Antennas, especially outdoor systems, act as lightening rods and care should be taken to avoid any hazards.
Items you will need
- 300-ohm twin-line antenna wire
- Electrical tape
- Wire cutter
- Knife or wire stripper
- soldering iron or gun
- 300-ohm to 75-ohm matching transformer (needed if the TV only has a 75-ohm coax cable input)
- tv set illustration image by Antalia from Fotolia.com